1. Field
The present disclosure relates to tire treads and more particularly to treads comprising grooves comprising closure devices for reducing the noise generated by air going into resonance inside these grooves during driving.
2. Description of Related Art
It is known that as a tire that is running comes into contact with a roadway in the contact patch, air is made to circulate in each groove, notably grooves of circumferential overall orientation. With the roadway, each groove forms a pipe having two open ends.
The air in this pipe forms a vibrating column of air the resonant frequency of which is dependent on the length separating the two ends of the pipe and therefore on the length of groove in contact with the roadway.
This resonance of the air in the grooves has the result of generating, in a vehicle fitted with these tires, a noise that can be heard inside the vehicle and outside the vehicle. These inside and outside noises usually correspond to a frequency of 1 kHz or thereabouts, which is a frequency to which the human ear is particularly sensitive.
In order to reduce such noise of resonance, it is known practice to arrange, in each circumferentially oriented or generally circumferentially oriented groove, a plurality of relatively thin flexible blades or membranes made of a rubber composition, each flexible blade or membrane occupying the entire cross section of the groove or, at least, a large proportion of this cross section in order to form a closure device.
Each flexible blade may extend from the bottom of the groove or may be fixed to at least one of the walls that delimit the said groove. Relatively thin means that each flexible blade is able to flex in order to open the cross section of the groove under the effect of a flow of liquid notably when driving in the wet.
Thanks to these flexible blades, the length of the column of air in each circumferential groove is reduced by comparison with the total length of the groove in the contact patch, and this leads to a change in the resonant frequency. The shift in frequency is towards resonant-frequency values to which the human ear is less sensitive.
Of course, in order to maintain the water-drainage function, when driving on a roadway covered with water, it is necessary for this membrane to be able to flex appropriately under the action of the pressure of the water and thus open the cross section of the groove in a way that is appropriate to allowing a sufficient flow of liquid.